The present invention relates to a pixel circuit of an electro-optical device for forming an image, to a method of driving the same, and to an electronic apparatus using the electro-optical device.
Known examples of electro-optical devices include a liquid crystal display device and an organic EL (electroluminescent) display device. The organic EL display device has received attention, because it has a structure in which an electro-optical element constituting a pixel is made of an organic EL material to have excellent characteristics, such as capability of emitting natural light, a wide viewing angle, a small thickness, a rapid response, and low power consumption, and can be made small and light by utilizing a peripheral circuit using a polysilicon TFT (thin film transistor).
However, there is luminance deviation among pixels in such an organic EL display device. For this reason, in order to suppress the luminance deviation among pixels, various driving methods based on a current programming method have been suggested (for example, see U.S. Pat. No. 6,229,506 B1).
According to the current programming method, since the TFT is operated in a saturation region of the TFT, it is possible to compensate for characteristic deviation of the TFT and an organic EL light-emitting element (hereinafter, referred to as an ‘OLED’).
However, in the current programming method according to the related art, there is a problem in that a current supplied to the OLED changes due to an insufficient amount of writing in a low gray-scale region or a change in an operating point of a driving transistor and thus gray-scale deviation occurs.
Accordingly, it is conceivable to provide ‘a current-programming-type time gray-scale method’.
This technology discloses a method of driving an electro-optical element in which a data current is supplied to a pixel having a storage capacitor, a driving transistor, and an electro-optical element, and the electro-optical element is driven on the basis of a driving current supplied from the driving transistor in accordance with the value of the data current. The method includes a step of supplying a data current having a predetermined value to the pixel to drive the electro-optical element, irrespective of input gray-scale data, and a step of adjusting the driving time of the electro-optical element on the basis of the gray-scale data. As a result, the insufficient amount of writing and the change in the operating point can be resolved.
However, when the suggested technology is applied to an actual OLED display panel, light-emitting times of pixels constituting a display panel should be individually controlled, so that the control operation or circuit structure becomes complicated.